Pressure sensors have wide applications in oilfield industry. Generally, pressure sensing elements are delicate transducers that are interrogated electrically. Pressure gauges, especially those for oilfield industry in harsh environments application, easily corrode or erode if exposed to downhole fluids without protection. Thus, they commonly require the protection of a working fluid such as silicon oil. The working fluid are commonly contains in bellows that introduce hysteresis.
Document U.S. Pat. No. 5,024,098 describes a pressure sensor useable in oil wells. The pressure sensor comprises a cell carrying a strain-measuring circuit. The cell is placed inside a body and is put into contact with the pressure to be measured. The cell has a hermetically sealed internal chamber inside which pressure is set to a low value. The outside surface of the cell is subjected to the pressure to be measured. The cell is constituted by two half-shells joining together according to a join plane. The cell is preferably made of sapphire, with the crystal axis of the sapphire being perpendicular to the join plane so as to obtain isotropic stresses. The strain-measuring circuit is deposited on a plane surface of one of the half-shells, parallel to the join plane. The strain-measuring circuit needs to be coupled to electrical means of interrogation. However, electrical means of interrogation is inappropriate in certain circumstances, for instance due to temperature constraints or unavailability of electrical power.
Further, when differential pressure measurements are required, many differential pressure gauges employ two absolute gauges to make independent measurements. Differential pressure is then calculated mathematically. A good accuracy is obtained when the differential pressure measurement represents a large fraction of the absolute pressures. However, in case of small differential pressure, the error associated with the differential pressure measurement rises significantly.